There are a number of applications that may need a switching regulator or switched mode power supply to operate in non-inverting buck or boost modes, transitioning relatively seamlessly between the two. Turning to FIG. 1, an example of a bridge 100, which can operate in boost and buck modes can be seen. This bridge 100 is generally an H-bridge, using switches S1 to S4, and an inductor L, which is coupled between the switching nodes of the H-bridge. In buck mode, switches S4 and S3 are closed and open, respectively, while pulse width modulation (PWM) signals are provided to switches S1 and S2. Alternatively, in boost mode, switches S1 and S2 are closed and open, respectively, while PWM signals are provided to switches S3 and S4.
A problem with bridge 100, however, is that there are some practical constraints that limit the ability to seamlessly transition between the buck and boost modes, namely, on-time and dead-time. Looking to buck mode, for example, switch S1 (or S2) cannot seamlessly reach 100% duty cycle. As can be seen in FIG. 2, switch S2, for example, has a minimum on-time TON (which is generally dictated by the physics of switch S2), and there is a dead-time TDEAD between a rising/falling edge of the PWM signal for switch S1 and the falling/rising edge of the PWM signal for switch S2. If the total on-time for switch S1 (for example) for a fixed frequency of 1/T (duty cycle in buck mode DBU times the period T) is greater than the period T minus this predetermined constraint period (DBU*T>T−2TDEAD−TON), then the gain (VOUT/VIN) of the regulator can deviate from an expected value.
Thus, there is a need for an improved switching regulator.
Some other conventional circuits are: U.S. Pat. No. 6,166,527; U.S. Pat. No. 6,037,755; and U.S. Patent Pre-Grant Publ. No. 2009/0039852.